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Environmental concerns have led to the development of automobile engines that are lightweight yet powerful. In consequence, the industry is now demanding an engine valve spring with higher fatigue strength and higher sag resistance. To meet the demands, the authors studied the influence of surface finishing and chemical compositions in Chromium-Silicon Alloy Steel on fatigue strength of steel wire for valve springs. The authors confirmed that the addition of silicon improves softening resistance while tempering, and electropolishing which eliminates surface flaws on wire are effective.

In recent years, efforts have “been undertaken to increase the stress load on spring materials and to decrease wire diameter in order to reduce weight. However, progress has “been slow due to the resulting increase in spring sag. This report describes the characteristics of steel wire subjected to a new strain method. After quenching and tempering, while the wire is still warm, strain is imposed on the wire to improve its sag resistance. Results show that sagging in springs made of this wire is approximately one half that of springs made of conventionally quenched and tempered wire of the same strength. Moreover, strain-imposed wire can be quenched and tempered to a lower strength than, yet have the same sag resistance as, extremely high-strength conventional wire. As a result, problems encountered when high strength material is used to improve sag resistance - such as damaged cutting tools and decreased shot peening effect can be avoided.